Centova Cast cannot operate without a valid license. Its cron job tries to run every 5 minutes, and if you do not have a valid license it will fail with a licensing error every time it runs, which cron will then email to you. If you are not using Centova Cast but do not want to uninstall it, please remove the Centova Cast cron job from /etc/crontab, or at least comment it out, so that the cron job does not continue running and generating these errors.